Vinyl Cyclopropyl compounds as precursors to fatty acid oxidation products

ABSTRACT

A nucleophile substituted unsaturated hydrocarbon based compound is prepared by reacting a compound of the formula: ##STR1## wherein R and R&#39; are hydrogen, alkyl, alkenyl, cycloalkyl, cycloalkenyl, aryl, aralkyl, alkoxyalkyl, alkoxy, alkylthioalkyl, or carboxyalkyl or carboxyalkenyl and X is a leaving group selected from the group consisting of chlorine, bromine, and iodine with a nucleophilic reagent.

Acknowledgement

Part of the invention was made under financial support of the NationalInstitute of Health.

This is a division of application Ser. No. 181,833, filed Aug. 27, 1980.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and reagent for the opening ofthe cyclopropyl ring of vinyl cyclopropyl compounds with thesimultaneous introduction of a nucleophile into the product compound.More particularly, the present invention relates to a method ofconverting unsaturated fatty acids containing a vinyl cyclopropylstructure to a hydroxy or hydroperoxy fatty acid.

2. Description of the Prior Art

Both the hydroxy and hydroperoxy derivatives of certain fatty acidsconventionally formed by the action of lipoxygenase enzymes on variousacid substrates are of medical interest because it is believed that theyplay significant roles in platelet pharmacology and in the inflammationof various tissues. For example, 12-L-hydroxy-5,8,10,14-eicosatetraenoicacid exhibits chemotatic activity on neutrophils. The correspondinghydroperoxy derivative as well as other hydroperoxy positional isomersmodulate the enzymes that control prostaglandin metabolism. E. J. Coreyet al, J. Am. Chem. Soc., 100, 1942 (1978) recently have described atotal synthesis of this compound.

Recently, two previously unknown monohydroxy C₂₀ fatty acids,5-L-hydroxy-6,8,11,14-eicosatetraenoic acid, whose chemical andenzymatic synthesis has recently been reported by E. J. Corey et al J.Am. Chem. Soc., 102, 1435 (1980), and8-L-hydroxy-9,11,14-eicosatetraenoic acid, have been isolated fromrabbit neutrophils. The structure of these compounds which contains acis, trans conjugated diene unit suggests that the mono-hydroxy acidcompounds are probably formed from the corresponding intermediatehydroperoxy compounds. In fact, it has been demonstrated that thehydroxy group of 5-L-hydroxy-6,8,11,14-eicosatetraenoic acid is derivedfrom molecular oxygen which is a finding consistent with theintermediacy of the corresponding hydroperoxy compound.

Interest in all of the above-discussed compounds as well as theirhydroperoxy intermediates has also been heightened by the postulate that5-L-hydroperoxy-6,8,11,14-eicosatetraenoic acid is a key intermediate inthe biosynthesis of leukotrienes. One member of this important group ofcompounds is leukotriene C, which is the slow reacting substance ofanaphylaxis, which causes prolonged smooth muscle contraction that isnot inhibited by conventional anti-histamines. Leukotriene C is alsobelieved to be intimately involved in the allergic response and may verywell be an important factor in certain types of asthma. Samuelsson et al(Proc. Nat. Acad. Sci, 76, 4275 (1979)) has suggested that leukotriene Cis biochemically prepared by a series of reactions in which5-L-hydroperoxy-6,8,11,14- eicosatetraenoic acid (an arachidonic acidhydroperoxide) is converted to leukotriene A, which is an epoxide.Leukotriene A is then converted to leukotriene C by reaction with thecysteine sulfur nucleophile. Even though the above suggested syntheticscheme has not been unequivocally established, nevertheless thefundamentally important function which the arachidonic acidhydroperoxide derivatives exhibit in inflammation and in certain formsof asthma is gaining increased recognition by the scientific community.

In view of the above developments there is an obvious need for a studyof the oxidative metabolism of unsaturated fatty acid compounds. Theoxidation products (endoperoxides and hydroperoxides) are evidentlyimportant factors in such major traumatic events as the inflammationprocess, blood platelet aggregation and consequently heart attack andstroke and the allergic response. Studies, therefore, directed to anunderstanding of the fundamental chemistry involved in fatty acidoxidation are believed to be important to a proper understanding ofthese pathological conditions. Previous attempts at synthesizing varioushydroxy and hydroperoxy derivatives of various unsaturated compoundshave been limited to enzyme catalyzed oxidation reactions of unsaturatedfatty acids and such non-enzymatic reactions as the reaction of singletoxygen generated by photolysis of molecular oxygen with the likes ofarachidonic acid. (Porter et al, J. Org. Chem., 44, 3177 (1979)).Another proposed method of synthesis involves the autooxidation ofarachidonic acid. However, in both known non-enzymatic oxidationreactions, a complex mixture of product compounds is obtained in lowyield which requires tedious chromatographic separation. A need,therefore, continues to exist for a method by which unsaturated fattyacid substrates can be oxidized to just a few, rather than a broadspectrum of possible corresponding hydroperoxy and hydroxy derivativesin good yield.

SUMMARY OF THE INVENTION

Accordingly, one objective of the present invention is to provide amethod by which unsaturated fatty acid compounds can be oxidativelyconverted by a nonenzymatic process to a selectively narrow spectrum ofhydroperoxy and hydroxy derivatives in good yield.

Another object of the present invention is to provide a method by whichhydroperoxy functionality can be introduced into an unsaturatedhydrocarbon compound. Yet another object of the invention is to providehydroperoxy and peroxy derivatives of unsaturated fatty acid compoundsfor a study of the role of these derivatives in several pathologicalconditions relating to the allergic response, inflammation and bloodplatelet aggregation.

Briefly, these objects and other objects of the present invention ashereinafter will become more readily apparent can be attained by amethod for synthesizing a nucleophile substituted unsaturatedhydrocarbon based compound by reacting a compound of the formula:##STR2## wherein R and R' independently are hydrogen, alkyl, alkenyl,cycloalkyl, cycloalkenyl, aryl, aralkyl, alkoxyalkyl, alkoxy,alkylthioalkyl, carboxyalkyl, or carboxyalkenyl, and X is a leavinggroup selected from the group consisting of chlorine, bromine andiodine, with a nucleophilic reagent.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The central feature of the present invention is based upon the discoverythat when a vinyl cyclopropyl compound bearing an appropriate leavingsubstituent is reacted with a nucleophile, the cyclopropyl ring isopened with the attachment of the nucleophile to a portion of themolecule. When the cyclopropyl ring is opened, a new olefinic bond isformed within the molecule which is conjugate to the olefinic bond ofthe vinyl group or an olefinic bond derived from the vinyl group. Thekey feature of the reactive vinylcyclopropyl substrate of the presentinvention is the attachment of a vinyl group on the cyclopropyl ring andthe presence of a leaving group at one of the other two carbon atoms ofthe cyclopropyl ring.

The vinyl cyclopropyl compound employed in the present invention has theformula: ##STR3## wherein substituents R and R' are hydrogen, alkyl offour to ten carbon atoms, alkenyl of four to ten carbon atoms containingat least one site of unsaturation, cycloalkyl, cycloalkenyl, aryl,aralkyl, alkoxyalkyl, alkoxy, alkylthioalkyl, carboxyalkyl,carboxyalkenyl, or the like.

Suitable specific examples of substituents include methyl, ethyl,propyl, butyl, hexyl, vinyl, propenyl, butenyl, hexenyl, cyclopentyl,cyclohexyl, cyclohexenyl, phenyl, naphthyl, benzyl, phenethyl and thelike.

Suitable leaving substituents (X) include bromo, chloro, iodo, and thelike.

The nucleophile which reacts with the vinylcyclopropyl substrate can beany nucleophile which will attack the cyclopropyl ring of the substrateor the vinyl group or an olefinic group conjugate to the vinyl group andbond to the site which it attacks and causes the opening of thecyclopropyl ring with the elimination of the leaving group (X) andformation of an olefinic bond in conjugation with the olefinic bond ofthe vinyl group or olefinic group derived from the vinyl group. Suitablenucleophilic agents which can react with the vinylcyclopropyl compoundinclude amines, organosulfides, organohydroperoxides, alkoxides, and thelike. An especially preferred nucleophile is a Ag⁺ salt/H₂ O₂ mixturewhich permits the introduction of a hydroperoxy substituent in theproduct compound. Suitable silver salts include the likes of silvernitrate, silver sulfate, silver trifluoroacetate, and the like.

The cyclopropyl ring opening reaction can be simply conducted byreacting the vinylcyclopropyl compound with the nucleophilic reagentunder nonstrenuous conditions. Thus, the reaction can be conducted attemperatures ranging from 0° to 40° C. in a solvent which dissolves thevinylcyclopropyl compound and facilitates the reaction of thenucleophilic reagent with the vinylcyclopropyl compound. Suitablesolvents include dialkyl ether compounds such as diethylether,dipropylether; dialkylformamide compounds such as dimethylformamide;acetonitrile; trifluoroethanol; dimethylsulfoxide and the like. Theamounts of vinylcyclopropyl compound and nucleophilic reagent employedin the reaction are not critical with the only objective being toconduct the reaction as far as possible to completion. Accordingly, theamount of nucleophilic reagent reacted with the vinylcyclopropylcompound can range from one to one hundred moles of nucleophilic reagentper mole of vinylcyclopropyl compound.

In a preferred embodiment of the present invention a fatty acidderivative containing a vinyl cyclopropyl structure of the formula:##STR4## is reacted with a nucleophilic reagent. A preferrednucleophilic reagent in the reaction is Ag⁺ salt/H₂ O₂ mixture whichintroduces a hydroperoxy substituent in the product. Accordingly, theuse of this particular nucleophilic reagent permits the synthesis of animportant group of hydroperoxy and hydroxy substituted unsaturated fattyacids or esters thereof which are found in biological systems. Thehydroperoxy group can also be introduced into the product molecule byusing an organohydroperoxide of the formula ROOH, wherein R is an alkylor aryl radical, in place of hydrogen peroxide in the above mentionednucleophilic reagent. The product of the reaction will contain anorganoperoxy group from which the R radical can be removed and replacedby hydrogen by conventional reaction methodology.

In the above formula of the unsaturated acid or ester derivative,suitable R" substituents include hydrogen; alkyl such as methyl, ethyl,pentyl, hexyl and the like; alkenyl containing at least one olefinicsite such as vinyl, propenyl, butenyl, hexenyl, heptenyl, CH₃ (CH₂) ₄--CH═CH--, CH₃ (CH₂)₄ CH═CH--CH₂ --CH═CH--, and the like, aralkyl andaralkenyl containing at least one olefinic site such as phenylvinyl,phenylpropenyl and the like. Suitable L substituents include alkylene ofthree to nine carbon atoms; alkylene of three to nine carbon atomscontaining at least one olefinic group such as --CH₂ CH═CHCH₂CH═CH(CH₂)₃ --, --CH₂ CH═CH--(CH₂)₃ --, and the like. Suitable R'"substituents include hydrogen and alkyl such as methyl, ethyl, butyl,pentyl, and the like; aryl; aralkyl; and the like. The leaving group Xis the same as defined above.

Another embodiment of the vinylcyclopropyl group containing fatty acidor ester compounds of the present invention includes compounds of theformula: ##STR5## wherein R", R'", L and X are as defined above.

In addition to the nucleophilic reagent described above for theintroduction of the hydroperoxy substituent in the fatty acid molecule,other nucleophilic reagents can be used as described earlier dependingupon the typoe of substituted fatty acid product desired. The conditionsemployed for the synthesis of the hydroperoxy or hydroxy substitutedfatty acid product are the same as those described above.

If it is desired to reduce the hydroperoxy group in the product fattyacid or ester molecule to the corresponding hydroxy group, this can bedone with the use of an appropriate reducing agent by conventionalreaction methodology. Suitable reducing agents include triarylphosphinessuch as triphenylphosphine trialkylphosphites, mercaptans,organosulfides and the like.

The utility of the method of the present invention is that it provides arelatively simple way of synthesizing compounds which have been shown orare suspected to possess significant biological properties relating toinflammation, the allergic response and blood platelet aggregation. Thepresent invention also provides a general synthetic technique by which acyclopropyl ring within a molecule can be opened to introduce anotherolefinic bond into the molecule while also introducing a substituent inthe molecule.

Having generally described the invention, a further understanding can beobtained by reference to certain specific examples which are providedherein for purpose of illustration only and are not intended to belimiting unless otherwise specified.

EXAMPLE 1 2-Hydroperoxy-3, 5-heptadiene

To a 5 ml round bottom flask are added 4 mg (.023 mmoles)2-bromo-3-(1-propenyl) methylcyclopropane, 270 μl 1 anhydrous ether and270 μl 90% HOOH (450 equivalents). In one addition, 510 mg silvertrifluoroacetate (100 equivalents) are added and the solution is stirredat room temperature for 15 minutes. The reaction is diluted with 15 mlether, washed once with 10 ml saturated NaHCO₃, and once with 10 mlsaturated NaCl solution, then dried over MgSO₄. After filtration, theproduct hydroperoxides are either converted to their correspondingalcohols or are concentrated on a rotovaporator and purified bychromatography (Water's μ porasil, 15% EtoAc/hexane). ##STR6## Thehydroperoxides obtained were reduced to the corresponding hydroxycompounds as follows:

2-Hydroxy-3,5-heptadiene

To a 25 ml round bottom flask is added the crude 15 ml ether solutioncontaining the product hydroperoxides. A few drops of water are added to`wet` the ether followed by approximately 100 mg triphenyl phosphine.The solution is stirred at room temperature for 15 minutes then driedover MgSO₄. After filtration, the solution is concentrated toapproximately 1 ml for capillary GC analysis. The hydroxy productsobtained compared favorably with authentic samples of the alcoholproducts.

The following reactions were conducted in the manner described above andshow the types of products obtained as a function of the structure ofthe vinyl cyclopropyl bromide compound used. ##STR7##

EXAMPLE 2

The following is the series of reactions employed to prepare thehydroperoxy compounds shown below. ##STR8##

Synthesis of Compound (B)

A mixture containing 32.4 gm (0.253 mol) of compound A 128 gm (0.506mol) CHBr₃ in a solvent system containing 56 ml CH₂ Cl₂, 90 ml 50% NaOHand 10 ml tetrabutylammonium hydroxide was stirred at 42° C. After 20 hrthe reaction was stopped and the entire reaction contents were extractedwith petroleum ether for 24 hr in a liquid-liquid continuous extractor.The petroleum ether solution was then washed several times with NH₄ Clsolution and with water. The organic solution was dried (MgSO₄) and thenthe solvent removed. The excess CHBr₃ was separated from the product bydistillation (40°-50°/0.1 mm) leaving a yellow oil weighing 40 gm (52%).The product could be further purified by column chromatography onFlorisil, eluting with 2% Et₂ O/98% C₆ H₁₄. The dibromide (B) wasthermally unstable and could not be distilled.

Synthesis of alcohol C

A solution containing 0.5 gm (2.0 mmol) dibromide (B) 2.0 gm (19.2 mmol)2,2-dimethylpropandiol and a catalytic amount of toluenesulfonic acid in9 ml of benzene was refluxed under a N₂ atmosphere. After four hr nostarting material remained and the reaction was diluted with 25 mlbenzene, washed with saturated NaHCO₃ solution and then three times withwater and finally dried (MgSO₄). The products were purified via columnchromatography on Florisil, eluting with 15% Et₂ O/85% C₆ H₁₄. C(398 mg,55%) was the most polar product.

Oxidation of compound C to the aldehyde

2.28 gm (6.37 mmol) (C) was oxidized with pyridinium chlorochromate at15° C. The reaction progress was monitored by TLC. After ten hr reactiontime all of (C) had been consumed. The crude product, an oil weighing1.72 gm (75%), crystallized from Et₂ O. The colorless solid (85° dec.)slowly decomposes at room temperature.

Synthesis of acetal D

n-Hexyl-triphenylphosphonium bromide, 7.26 gm (17 mmol), was suspendedin 52 ml of freshly distilled THF under a N₂ atmosphere at -20° C. Tothis was added dropwise 7.0 ml of a 2.4M (16.8 mmol) solution ofn-butyllithium. The resulting orange colored ylid was stirred at -20° C.for 20 min, then the temperature was raised to 0°-5° C. To this ylidsolution was added dropwise 1.52 gm (4.25 mmol) aldehyde dissolved in8.5 ml dry THF. The resulting solution was then stirred for 2.25 hr at0°-5° C. and then quenched by the addition of 8 ml cold H₂ O. Thereaction mixture was diluted with Et₂ O and washed with brine and thenwater. The organic solution was dried (MgSO₄). The solvent was removedleaving an oil which was purified via cold column chromatography (-10°C.) on Florisil and 1% Et₂ O/99% C₆ H₁₄ eluant. The product D weighed1.29 gm (71%).

Reaction of Compound D with methyl lithium

1.29 gm (3.04 mmole) D in 30 ml ether was cooled to -78° C. and to thissolution was added 8 mmol methyllithium-lithium bromide over 4 min. Themixture was stirred for 20 min and quenched by the slow addition of 1 mlof water. The monobromide acetal was purified by cold columnchromatography (-10° C.) eluting with 1% ether, 99% hexane. Yield: 0.836gm (80%).

Synthesis of Compound E

A solution containing 96 mg (0.28 mmol) monobromide acetal in 0.5 ml THFand 3.5 ml of 88% formic acid were stirred at 0° under a N₂ atmospherefor 31 hr. At this time, all of the monobromide acetal was consumed. Amix of cold brine and ether was added to the reaction. The organic layerwas washed three times with brine and then neutralized with saturatedbicarbonate solution. The organic solution was dried (MgSO₄) and keptcold. Purification via cold column chromatography (-10° C.) on Florisilwith 4% Et₂ O/96% C₆ H₁₄ eluent yielded 64 mg (88%) aldehyde (E). Thealdehyde slowly decomposes at room temperature and should be stored at-20° C.

Synthesis of Wittig Product F

The phosphonium salt 0.370 gm (0.74 mmol) that was previously dried at100° C./0.1 mm was dissolved in 3.5 ml of freshly distilled THF at roomtemperature and under a N₂ atmosphere. To this was added dropwise 1.4 ml(0.70 mmol) of 0.5M THF solution of potassium t-butoxide. The resultingylid solution was stirred at room temperature for 15 min and then thetemperature was lowered to 0°. A solution containing 1.6 ml dry THF and63 mg (0.24 mmol) aldehyde was added dropwise. The resulting solutionwas stirred at 0° for three hr. The reaction was quenched by thedropwise addition of 1 ml cold H₂ O followed by addition of a cold brineand ether mixture. The organic phase was dried (MgSO₄) and the solventremoved leaving an oil. The product was purified via cold columnchromatography (-10° C.) on Florisil, eluting with 4% Et₂ O/96% C₆ H₁₄.The purified product 82 mg (85%) was not stable at room temperature forperiods longer than a few hours.

Reaction of Compound F with Ag⁺ /H₂ O₂

In 6.6 ml of dry ethyl ether at 0° C. was dissolved 40 mg (0.1 mmol)bromide (F). To this solution was added 0.95 ml 90% H₂ O₂ (36.3 mmol) inone portion. The solution of F and H₂ O₂ was allowed to warm to slightlybelow room temperature and then 0.758 gm (3.5 mmol) of silvertrifluoroacetate was added in one portion. A yellowish precipitate ofAgBr formed almost immediately. The reaction was allowed to stir forfive to ten min and then was quenched by the addition of a cold mixtureof aqueous NaHCO₃ and ether. The ether solution was washed twice withthe bicarbonate and then dried (MgSO₄). The products were purified viacold column chromatography (-10°) on Florisil eluting with 15% Et₂ O/85%C₆ H₁₄. The two products isolated 25 mg (71%) gave a positive peroxidetest to a ferrous thiocyanate spray reagent on TLC (silica gel plates,50 % Et₂ O/50% C₆ H₁₄). The two products had identical HPLC elutionorder and retention volumes as the 12 and 8-hydroperoxy eicosatrienoicacid methyl esters synthesized previously.

Having now fully described the invention, it will be apparent to one ofordinary skill in the art that many changes and modifications can bemade thereto without departing from the spirit or scope of the inventionas set forth herein.

What is claimed as new and is intended to be secured by Letters Patentis:
 1. A method of synthesizing a nucleophile substituted unsaturatedhydrocarbon based compound, comprising:reacting a compound of theformula: ##STR9## wherein R and R' are hydrogen, alkyl, alkenyl,cycloalkyl, cycloalkenyl, aryl, aralkyl, alkoxyalkyl, alkoxy,alkylthioalkyl, carboxyalkyl, carboxyalkenyl, and X is a leaving groupselected from the group consisting of chlorine, bromine and iodine witha nucleophilic reagent selected from the group consisting of an amine,an organosulfide, an alkoxide, or an organohydroperoxide.
 2. The methodof claim 1, wherein said leaving group X is bromine.
 3. The method ofclaim 1, wherein said reaction is conducted at a temperature of 0° to40° C.
 4. The method of claim 1, wherein said reaction is conducted in asolvent of a dialkylether, a dialkylformamide, acetonitrile,trifluoroethanol, or dimethylsulfoxide.
 5. A method for synthesizing anucleophile substituted fatty acid derivative, comprising:reacting avinyl cyclopropyl group containing fatty acid or ester of the formula:##STR10## wherein R" is a hydrogen, alkyl, aralkyl, or alkenyl oraralkenyl containing at least one olefinic site; L is alkylene of 3 to 9carbon atoms, optionally containing at least one olefinic site; R'" ishydrogen, alkyl, aryl or aralkyl and X is a leaving group selected fromthe group consisting of chlorine, bromine, and iodine and a nucleophilicreagent selected from the group consisting of an amine, anorganosulfide, an alkoxide or an organohydroperoxide.
 6. The method ofclaim 5, wherein in said vinyl cyclopropyl compound reactant, saidsubstituent R'" is methyl, R" is CH₃ (CH₂)₄ CH═CH--, X is bromine and Lis --(CH₂)₆ --.
 7. The method of claim 5, wherein said group R isn-butyl, said radical --L-- is --CH₂ CH═CHCH₂ CH═CH(CH₂)₃ -- and R' ismethyl.
 8. A vinyl cyclopropyl group containing fatty acid or ester ofthe formula: ##STR11## wherein R" is hydrogen, alkyl, aralkyl, oralkenyl or aralkenyl containing at least one olefinic site; L isalkylene of 3 to 9 carbon atoms, optionally containing at least oneolefinic site; R'" is hydrogen, alkyl, aryl or aralkyl and X is aleaving group selected from the group consisting of chlorine, bromineand iodine.
 9. A method for synthesizing a nucleophile substituted fattyacid derivative, comprising:reacting a vinylcyclopropyl group containingfatty acid or ester of the formula: ##STR12## wherein R", R'", L and Xare as defined in claim 8 with a nucleophilic reagent selected from thegroup consisting of an amine, an organosulfide, an alkoxide, or anorganohydroperoxide.
 10. A vinyl cyclopropyl group containing fatty acidor ester of the formula: ##STR13## wherein R", R'", L and X are asdefined in claim 8.